Wednesday, January 13, 2010

Some 2 million schoolchildren in the Beijing region enjoyed an extra day off at New Year’s in January 2010 while authorities put some 300,000 people to work clearing streets. Up to 30 centimeters (12 inches) of snow fell on the capital city of Beijing and nearby port city of Tianjin, closing schools, clogging roads, and canceling flights. Although not as bad as the 2008 freeze that ruined travel plans for millions of Chinese trying to visit family for the lunar new year, this snowstorm was described as the heaviest snow to fall on Beijing in almost 60 years.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this true-color image on January 4, 2010. Snow cover encircles Bo Hai and extends to the north and west of that water body. Snow also covers Beijing, Tianjin, and a constellation of smaller settlements. The large cities leave big gray splotches on the blanket of snow, and the smaller cities make small gray dots. Snow caps the mountains north and west of Beijing, but the snow cover gradually fades southwest of Beijing and Tianjin. Cloud streets—clouds arranged in neat rows—similar to those observed over Hudson Bay and the Great Lakes float over Bo Hai.
Unlike the deep freeze of 2008, this storm was not expected to cause weeks-long fuel shortages for northern China, although disruptions to transportation and damage to greenhouses were expected to raise food prices. Temperatures in Beijing were expected to fall to -18 degrees Celsius (-0.4 degrees Fahrenheit) on the night of January 5, 2010, and some of the northernmost parts of China might experience temperatures as low as -32 degrees Celsius (-25.6 degrees Fahrenheit) by the following morning

If you live nearly anywhere in North America, Europe, or Asia, it’s no news that December 2009 and early January 2010 were cold. This image illustrates how cold December was compared to the average of temperatures recorded in December between 2000 and 2008. Blue points to colder than average land surface temperatures, while red indicates warmer temperatures. Much of the Northern Hemisphere experienced cold land surface temperatures, but the Arctic was exceptionally warm. This weather pattern is a tale-tell sign of the Arctic Oscillation.
The Arctic Oscillation is a climate pattern that influences winter weather in the Northern Hemisphere. It is defined by the pressure difference between air at mid-latitudes (around 45 degrees North, about the latitude of Montreal, Canada or Bordeaux, France) and air over the Arctic. A low-pressure air mass usually dominates the Arctic, and while higher pressure air sits over the mid-latitudes. This pressure difference generates winds that confine extremely cold air to the Arctic. Sometimes, the pressure systems weaken, decreasing the pressure difference between the Arctic and midlatitudes and allowing chilly Arctic air to slide south while warmer air creeps north. A weaker-than-normal Arctic Oscillation is said to be negative. When the pressure systems are strong, the Arctic Oscillation is positive.
Throughout December 2009, the North Atlantic Oscillation was strongly negative, said the National Weather Service. This image shows the impact of the negative Arctic Oscillation on land surface temperatures throughout the Northern Hemisphere as observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Cold Arctic air chilled the land surface at midlatitudes, while Arctic land, such as Greenland and Alaska, was much warmer than usual.

Located over the continental shelf of southeastern South America is one of the world’s most productive and complex marine ecosystems. Covering about 1.2 million square kilometers (4.6 million square miles) of coastal waters, the Patagonia Large Marine Ecosystem stretches from the Rio de le Plata (a wide estuary at the mouth of the Paraná River) to the southern tip of the continent.
In November 2009, as summer approached in the Southern Hemisphere, the foundation of the ecosystem’s food web—plant-like microorganisms called phytoplankton—bloomed expansively, brightening the waters with living ribbons of color. The image on the left shows the monthly average chlorophyll concentration in milligrams per cubic meter of water. High chlorophyll concentrations (yellow) mean large populations of phytoplankton, which use chlorophyll and other pigments to capture sunlight for photosynthesis.
The sea surface temperature image (right) reveals one of the reasons for the region’s productivity: the convergence of two wind-driven ocean currents. The warm, salty Brazil Current meanders south over the continental shelf, where it meets the cold, less-salty Falklands/Malvinas Current, a north-flowing branch off the Antarctic Circumpolar Current.
In the spring and summer, the convergence zone occurs at about the latitude of the Rio de la Plata, which is where it seems to be based on the water temperatures shown in the sea surface temperature image. Blues and purples (cooler water) dominate the image south of the estuary, while pinks and yellows (warmer water) dominate the image north of there.
The convergence of two water masses of different temperatures and saltiness enhances mixing of the water, both vertically and horizontally. Vertical mixing brings nutrient-rich water up from deeper in the ocean, restocking surface waters.

These images are made from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite in November 2009. Aqua has been collecting data on the ecological and physical state of the ocean since its launch in 2002. Monthly maps of chlorophyll and sea surface temperature from Aqua are available in Global Maps on the Earth Observatory.

Rain bands from a prevailing easterly wave over peninsula were now being propagated north-northeast as overnight showers wetted many places over Lakshadweep and a few places over north interior Karnataka.

Isolated rainfall occurred over Tamil Nadu, south interior Karnataka and Andhra Pradesh, according to an update from the Chennai Regional Met Centre.

Forecast for the next two days said that rain or thundershowers would occur at many places over Telangana and at a few places over coastal Andhra Pradesh, Rayalaseema, Lakshadweep and Karnataka. Isolated rain or thundershowers have been forecast over Tamil Nadu, Puducherry and Kerala.

Meanwhile, there has been some respite from the ultra low night temperatures in the north and northwest as an incoming westerly trough began exerting influence over regional weather.

Minimum temperatures were below normal by only 2 to 4 deg Celsius over parts of the Indo-Gangetic plains on Monday night, an update by India Meteorological Department (IMD) said on Tuesday.

They were even above normal by 4 to 6 deg Celsius over most parts of Rajasthan, Gujarat and West Madhya Pradesh, which constitute the gateway for the westerly trough. The lowest minimum over the plains of the country was 2.2 deg Celsius recorded at Amritsar in Punjab.

But maximum temperatures continued to wallow below normal by 8 to 12 deg Celsius over most parts of Uttar Pradesh, Bihar, Punjab, Haryana and Delhi, which lay farther downstream of the westerly system.

Calming influence

Compared to this, the proximity to the approaching system had its calming influence on north Rajasthan and north Madhya Pradesh where the maximum were only 4 to 6 deg below normal.

They were above normal by 2 to 3 deg Celsius over some parts of interior Orissa, Chhattisgarh, Vidarbha, coastal Andhra Pradesh, Saurashtra and Kutch due to the confluence of moisture-bearing winds from the south and the west.

Fog conditions were prevailing over many parts of Haryana, Uttar Pradesh, Bihar, sub-Himalayan West Bengal and west Assam through Monday night and Tuesday morning. Outlook until Friday spoke about the possibility of fog/dense fog in the morning towards the east of the plains, mainly over parts of east Uttar Pradesh and Bihar, during the next 24 hours (Wednesday).

Thereafter, its density and duration may decrease. Cold day conditions are expected to occur over parts of Punjab, Haryana, Uttar Pradesh and Bihar during the next three days.

Minimum temperatures over northwest India will increase by 2 to 3 deg Celsius during the next 24 hours but could fall thereafter with the warmth of the westerly trough moving away to the east.

Scattered to fairly widespread rain or snow has been forecast over the western Himalayan region during next two days. Scattered rainfall is likely over parts of the plains of northwest and adjoining central India until Thursday.

Rain for Northwest

The US Centres for Environmental Prediction (NCEP) maintained its outlook for a wave of scattered peninsular rains propagating north-northeast to cover the entire peninsula during January 12 to 19.

The following week (January 20 to 28) is forecast to bring about widespread to fairly widespread rainfall over the entire north, northwest, east and northeast India, including parts of central India but possibly excluding Gujarat.

This would be brought about by repeat western disturbances invading northwest India with rain-making troughs in tow, presumably remainder waves from snow storms hitting western Europe and downstream central Asia and West Asia.

The density and duration of seasonal fog over the Indo-Gangetic plains may recede from Wednesday as the region comes under the influence of a westerly trough and associated change in wind direction.

The colder north to northwesterlies would get replaced by warmer westerlies to southwesterlies as the system rolls in across the border on Wednesday.

It is likely that a secondary circulation may get formed over the north-west as the westerlies sweep north Arabian Sea and mop up available moisture.

This moisture is likely to emptied as rain over the plains even as India Meteorological Department (IMD) saw the prospects of confluence of westerly and easterly winds over central India. This could add to the instability of atmospheric conditions and associated weather.

The trough in the westerlies is seen affecting northwest India on Wednesday and Thursday, the IMD said. It saw fog to dense fog conditions prevailing in the morning over parts of Indo-Gangetic plains during the next 24 hours.

Cold day conditions (with lower maximum day temperatures) will occur over parts of Punjab, Haryana and Uttar Pradesh during the next two days.

The warm westerly system will cause minimum temperatures also to increase by 2 to 4 deg Celsius during this period, leading to abatement of cold wave conditions.

The impact of the westerly system would be the most over the windward side of the western Himalayan region since the air would be made to rise against the mountain heights, cool and be brought down as either rain or snow.

The IMD has forecast scattered to fairly widespread rain or snow over the western Himalayan region mainly on Tuesday and Wednesday. Scattered rainfall is likely over parts of plains of the northwest and adjoining central India during this phase.

On Sunday, the minimum temperatures were below normal by 2 to 4 deg Celsius over parts of Punjab, west Rajasthan, north Madhya Pradesh, east Uttar Pradesh and Bihar.

The lowest minimum temperature of 1.2 deg Celsius was recorded at Amritsar on Sunday night. Cold wave conditions have been prevailing over isolated pockets of west Rajasthan, north Madhya Pradesh, east Uttar Pradesh and Bihar.

The maximum temperatures were below normal by 7 to 11°C over most parts of Punjab, Haryana, Delhi and Uttar Pradesh and by 4 to 6 deg Celsius over many parts of north Rajasthan, Bihar and some parts of northwest Madhya Pradesh.

In this manner, cold day conditions prevailed over most parts of Punjab, Haryana, Delhi, north Rajasthan and Uttar Pradesh.

But the westerly system will keep moving to the east across the plains, bringing the ‘steaming head' marked by lower pressure and ascending air ahead to drop some rain over east and northeast India. In the process, it might also run into the easterly flows straying into east and central India.

Cold northwesterlies would promptly fill the region vacated by the westerly system and once again lower the mercury level progressively over north and northwest India.

The IMD has forecast a fall in minimum temperatures over northwest, central and east India until January 16 up to which forecasts were available.

Meanwhile, an easterly wave has been affecting south peninsular India. Rainfall has occurred at a few places over coastal Tamil Nadu and coastal Karnataka during the 24 hours ending Monday morning.

Scattered rainfall may occur over parts of south peninsular India during the next three days, the IMD said, which is in agreement with the outlook of international models.

The Chennai Met Centre has forecast rain or thundershowers at a few places over coastal Tamil Nadu, Puducherry, and coastal Karnataka over the next two days. Isolated rain or thundershowers could occur over interior Tamil Nadu, Kerala, Andhra Pradesh, Lakshadweep and interior Karnataka.